These mounts, true earthquake resistant supports, are mainly composed of two detached monoblock elements and are intended to be interposed between the infrastructure and the superstructure of all sorts of buildings and erected constructions, for the purpose of allowing these constructions to avoid being subjected to the effects of the most violent earthquake attacks.
The earthquake resistant devices known to date are of two distinct types: they are either based on a possibility of sliding with friction allowing limited displacement, or designed on the basis of elastomeric blocks, often hooped, the distortion of which is put to use. In the first case displacement of the building is not damped out and substantial lateral displacements may give rise to extremely high impacts which may be the cause of breakage of the earthquake resistant device itself, or even of the building to be protected. The characteristics of natural or synthetic elastomeric blocks, hooped in the second case, change over time, which logically should lead to them being replaced periodically, and what is more these devices do not make it possible to control completely the amplitude of the movements due to the earth tremors.
The devices described in the French Patent Letters 2,625,763, 2,601,716 and in the U.S. Pat. No. 5,131,195 filed by the same inventor partly eliminate these drawbacks.
Indeed, they make it possible, at the same time, to damp out both vertical and lateral movements brought about by an earthquake, and to control the amplitude of these movements, while braking them. Furthermore, they are made up of materials which are extremely stable with time, and which perfectly resist differences in temperature, microorganisms, and chemical attack. These devices are made up of two monoblock elements produced from a hard, rotproof material, which has great resistance to abrasion, these elements being respectively secured to the infrastructure and to the superstructure of the building, the lower element being made up of a horizontal rubbing plate including a cone frustum at its center, the upper element being made up of a circular cap having its concavity pointing towards the bottom and capping the lower element so that the blind end of the concavity rests on the top of the cone frustum and the lower edges rest on the rubbing plate of the lower element, an annular space between the two elements allowing relative lateral displacement, said elements being supplemented by one or two rings made from a material which is also rotproof and has high impact-damping characteristics, these rings being secured to the internal lateral wall of the upper element and/or to the lateral wall of the cone frustum of the lower element and filling all or some of the annular space.
However, the design of these devices means that they are not very effective for earthquakes having an amplitude of less than 0.2 on the Richter scale. This is due to the coefficient of friction of the materials used, which index hitherto has been close to 0.2. Now, current legislation requires a coefficient of less than or equal to 0.05 for this type of device, precisely so that they are capable of acting even for tremors of very low amplitude.